1. Field of the Invention
The present invention relates to an optical pattern extracting apparatus and, more particularly, to an optical pattern extracting apparatus suitably applied to an OCR (Optical Character Reader) for recognizing handwritten kanji or Chinese characters.
2. Description of the Related Art
In an apparatus (OCR) for reading handwritten characters, various types of pattern recognition techniques have been utilized. No remarkable technique having a low error rate has been established in a kanji OCR.
U.S. Pat. No. 3,252,140 to Lemay discloses a technique wherein a large number of reference feature masks having elemental features constituting character patterns are prepared, a character image to be recognized is caused to overlap feature masks to optically detect a degree of correlation, and each character is specified on the basis of correlation information.
The prepared reference feature masks are produced to display character images of correct styles at proper positions and have appropriate thicknesses. When positions, sizes and thicknesses of, e.g., handwritten characters are changed, and styles are deformed, the degree of matching between the character images and the feature mask is lowered to increase an error rate in character identification.
In order to recognize complex characters such as kanji characters, a very large number of feature masks must be prepared, and collation between the characters and the feature masks is time-consuming.
U.S. Pat. No. 4,573,198 to Anderson discloses a technique wherein a character image is optically Fourier-transformed and is collated with reference feature patterns in a frequency region. A processing system independent of positional variations in character images requires a coherent light source since this processing system is a Fourier transformation optical system, thus resulting in a bulky apparatus.